1. Field of the Invention
The present invention relates to a heating device for and a heating method of processing a substrate coated with a coating liquid by a heating process.
2. Description of the Related Art
A coating and developing system, which applies a resist to a semiconductor wafer (hereinafter, referred to as “wafer”) and processes the wafer processed by an exposure process by a developing process, is used as a resist pattern forming system for forming a resist pattern on a wafer or a glass substrate for a LCD (liquid crystal display). The coating and developing system includes a heating device called a baking device. A heating device for heating, for example, a wafer coated with a liquid resist film dries the liquid resist film by removing a solvent contained in the liquid resist film.
The inventors of the present invention are making an effort to use a heating device, which covers a space extending over a heating plate for heating a wafer to form an air passage and generates a unidirectional air flow from an entrance opening at one end of the gas passage toward an exit opening at the other end of the gas passage, for carrying out a heating process. When such a unidirectional air flow is generated in the air passage, the adhesion of particles of sublimates sublimated from the liquid resist to a wafer W can be reduced.
FIG. 18 shows a heating device in which a unidirectional flow is generated. Shown in FIG. 18 are a box 10, an opening 10a through which a wafer is carried into and carried out of the box 10, and a shutter 10b for covering the opening 10a. Shown also in FIG. 18 are a base plate 11, a heating plate 12, and a cooling plate 13 capable of moving toward the heating plate 12 on the base plate 11 to cool a wafer W. A gas supply device 14 and a gas discharge device 15 are disposed on the base plate 11 at a position on the front side of the heating plate 12 and at a position on the rear side of the heating plate 12, respectively.
Lifting mechanisms 16 and 17 respectively for vertically moving pins 16a and 17a are disposed in a space under the base plate 11. The lifting mechanism 16 moves the pins 16a vertically to transfer a wafer W from an external carrying mechanism, not shown, advanced through the opening 10a into the box 10 to the cooling plate 13 and to transfer a wafer W from the cooling plate to the external carrying mechanism. The lifting mechanism 17 moves the pins 17a vertically to transfer a wafer W between the heating plate 12 and the cooling plate 13. A top plate 18 can be moved vertically by a lifting mechanism 18a. 
A heating process to be carried out by this heating device will be described with reference to FIG. 19. As shown in FIG. 19(a), the heating plate 12 is covered with the top plate 18, the heating plate 12 is heated at a predetermined temperature, and a wafer W is delivered to the cooling plate 13. Then, as shown in FIG. 19(b), the top plate 18 is raised, the cooling plate 13 is advanced into a space extending between the top plate 18 and the heating plate 12, and then the wafer W is transferred from the cooling plate 13 to the heating plate 12. Then, as shown in FIG. 19(c), the cooling plate 13 is retracted to a position near the heating plate 12, and the top plate 18 is lowered near to the heating plate 12. In this state, the gas supply device 14 and the gas discharge device 15 are operated to generate a unidirectional gas flow from the gas supply device 14 toward the gas discharge device 15, and the wafer W is subjected to predetermined heating process. The top plate 18 is raised, and then the wafer W processed by the heating process is transferred from the heating plate 12 to the cooling plate 13. Subsequently, the wafer W is transferred from the cooling plate 13 to a carrying means, not shown, and then the carrying means carries the wafer W to the next process.
A resist pattern forming system provided with heating devices like this heating device requires the heating devices to be formed in a small thickness and to be stacked in layers to increase the throughput thereof. This heating device has a cooling mechanism including a cooling pipe embedded in the cooling plate 13 or attached to the lower surface of the cooling plate 13 to pass a cooling liquid through the cooling pipe. Therefore, the cooling plate 13 has a thickness on the order of 10 mm. Therefore, the thickness of a space extending between the heating plate 12 and the top plate 18 needs to be 10 mm or above taking into consideration the thickness of the cooling plate 13 and the thickness of a space necessary for transferring a wafer W to achieve transferring the wafer W between the heating plate 12 and the cooling plate 13. Consequently, it is difficult to form the heating device in a small thickness.
When the space extending between the heating plate 12 and the top plate 18 is thick, external air flows into the space between the heating plate 12 and the top plate 18 and disturbs the unidirectional air flow in the space. Consequently, the sublimates cannot be satisfactorily carried away from the space by the unidirectional air flow. Therefore, the top plate 18 is supported vertically movably, the top plate 18 is raised when the wafer W is transferred between the heating plate 12 and the cooling plate 13, and the top plate 18 is lowered to a predetermined position when the wafer W is processed by the heating process. However, when the top plate 18 is supported vertically movably, a space for installing the lifting mechanism and a space in which the top plate 18 is moved vertically are necessary, which obstructs reducing the thickness of the heating device.
In view of the foregoing problems, the inventors of the present invention are making studies of building a thin heating device by abandoning carrying a wafer W by the cooling plate 13 to reduce the vertical dimension of the space between the heating plate 12 and the top plate 18, abandoning vertically moving the top plate 18 and abandoning transferring a wafer W between the cooling plate 13 and the hot plate 12. A substrate carrying structure mentioned in Patent document 1 carries a substrate to a heating plate by keeping the substrate afloat by the pressure of a gas spouted through many small ports formed in the bottom wall of a structure defining a substrate carrying path without using plates and arms.
The structure mentioned in Patent document 1 spouts the gas in the moving direction of the substrate. Since any frictional force acts on the floating substrate, the substrate is unstable and is moved by a slight force. Therefore, the substrate is liable to drift longitudinally or transversely when the gas is spouted in the moving direction. Consequently, this known structure has difficulty in stabilizing and stably moving a wafer and in stopping the wafer W at a desired position. Thus this known structure is unpractical.
Patent document 1: JP-A 57-128940, p. 2, I. 2, upper right-hand col. to p. 2, I. 4, lower left-hand col.